SEMICONDUCTOR MEMORY DEVICE AND METHOD OF MANUFACTURING THE SAME
In a memory cell including an nMIS for memory formed on the sides of an nMIS for select and an nMIS for select via dielectric films and a charge storage layer, the thickness of a gate dielectric under the gate longitudinal direction end of a select gate electrode is formed thicker than that of the gate dielectric under the gate longitudinal direction center and the thickness of the lower layer dielectric film that is positioned between the select gate electrode and the charge storage layer and is nearest to a semiconductor substrate is formed 1.5 times or below of the thickness of the lower layer dielectric film positioned between the semiconductor substrate and the charge storage layer.
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The present application claims priority from Japanese Patent Application No. JP 2007-218498 filed on Aug. 24, 2007, the content of which is hereby incorporated by reference into this application.
TECHNICAL FIELD OF THE INVENTIONThe present invention relates to a semiconductor memory device and a technology of manufacturing the same, in particular, to a technology effective when applied to a semiconductor memory device having an MONOS (Metal Oxide Nitride Oxide Semiconductor) memory cell in which a nitride film is a charge storage layer.
BACKGROUND OF THE INVENTIONAs a nonvolatile semiconductor memory device to which data can be written and erased electrically, an EEPROM (Electrical Erasable and Programmable Read Only Memory) is used now. In the memory cell of the nonvolatile semiconductor memory device represented by a flash memory, an charge accumulation region represented by a conductive floating gate electrode surrounded by an oxide film or a charge-trapping dielectric film is arranged under the gate electrode of an MIS (Metal Insulator Semiconductor), and an charge is accumulated in this charge accumulation region as memory information, and the same is read as the threshold voltage of the MIS transistor.
As the memory cell in which a charge-trapping dielectric film is a charge accumulation region, there is a memory cell of the MONOS method. In particular, a split gate type memory cell in which one memory cell includes two gate electrodes of a memory gate electrode and a select gate electrode is used widely in late years. Because the split gate type memory cell uses a charge-trapping dielectric film as its charge accumulation region, it can accumulate a charge discretely, and thereby it has superior reliability of the data retention. Further, because it has superior reliability of the data retention, the oxide films formed above and under the charge-trapping dielectric film can be made thin, therefore, it has advantages including the low voltage of program/erase operations and the like. Furthermore, by using split gate type memory cell, hot electrons can be injected into the charge-trapping dielectric film by SSI (Source Side Injection) method whose injection efficiency is excellent, and data can be written at a high speed and at a low current. Moreover, it has the advantage that peripheral circuits can be made small because the control of its program and erase operations is simple. The charge-trapping dielectric film is a dielectric film enabling charge accumulation, and, as an example, there is a silicon nitride film.
The cell structure of the split gate type memory cell is roughly divided into two kinds shown in
An advantage of the above first memory cell is that because there is the ONO film between the memory gate electrode MG and the select gate electrode CG, it is easy to secure the withstand voltage between the memory gate electrode MG and the select gate electrode CG, and the distance between them can be made as short as the thickness of the ONO film. Since the distance between the memory gate electrode MG and the select gate electrode CG can be made short, the gap resistance of the channel region under an interval between the memory gate electrode MG and the select gate electrode CG becomes small, and it is possible to obtain a larger read current than that in the above second memory cell. Meanwhile, in
When program is performed by the SSI method, in the split gate type MONOS memory cell, a program disturb becomes a problem. The program disturb herein is a phenomenon in which when a certain memory cell is selected, and the memory cell is programmed, the voltage applied to the selected memory cell is also applied to unselected memory cells that are connected to the same wire and are not selected, and the unselected memory cells perform weak program and weak erase operations, and data is lost slowly. In the program by the SSI method, a high voltage is applied to both the source line to which source regions of a plurality of memory cells are connected, and the memory gate line to which memory gate electrodes of a plurality of memory cells are connected. Therefore, there are unselected memory cells to which the high voltage of program is applied in both the source regions and the memory gate electrodes, and in the unselected memory cells, weak program in which electrons are injected into the charge accumulation region occurs, which becomes a problem.
As a method to solve the disturb, there is a method to reduce the number of memory cells to be connected to the same source line and the same memory gate line. However, in this method, it is necessary to divide one line into a plurality of lines, and increase the numbers of drivers to drive the lines, therefore, the area of memory module increases.
An object of the present invention is to provide a technology that can improve disturb tolerance at the time of program by the SSI method in a split gate type MONOS memory cell.
The above and other objects and novel characteristics of the present invention will be apparent from the description of this specification and the accompanying drawings.
SUMMARY OF THE INVENTIONThe typical ones of the inventions disclosed in this application will be briefly described as follows.
According to the present invention, there is provided a semiconductor memory device having a split gate type MONOS memory cell, including a select gate electrode of a field effect transistor for selection, a memory gate electrode of a field effect transistor for memory, a gate dielectric formed between a semiconductor substrate and the select gate electrode, a lower layer dielectric film formed between the semiconductor substrate and the memory gate electrode and between the select gate electrode and the memory gate electrode, a charge holding dielectric film of a laminating structure comprising a charge storage layer and an upper layer dielectric film, wherein the thickness of the gate dielectric under the gate longitudinal direction end of the select gate electrode is thicker than the thickness of the gate dielectric under the gate longitudinal center of the select gate electrode, and the thickness of the lower layer dielectric film that is positioned between the select gate electrode and the charge storage layer and is nearest to the semiconductor substrate, is 1.5 times or below of the thickness of the lower layer dielectric film between the semiconductor substrate and the charge storage layer.
According to the present invention, there is provided a method of manufacturing a semiconductor memory device having a split gate type MONOS memory cell, including a step of forming a gate dielectric of a field effect transistor for selection on the main surface of a semiconductor substrate, a step of forming a select gate electrode of a field effect transistor for selection comprising a first conductive film on the gate dielectric, a step of removing the gate dielectric in other regions than the gate dielectric under a select gate electrode, a step of performing an oxidation process to the semiconductor substrate, and, by performing oxidization process to a semiconductor substrate, forming the thickness of the gate dielectric under the gate longitudinal direction end of the select gate electrode thicker than that of the gate dielectric under the gate longitudinal center of the select gate electrode, a step of exposing the main surface of the semiconductor substrate while leaving the gate dielectric under the select gate electrode, a step of forming a lower layer dielectric film on the main surface of the semiconductor substrate, a step of forming a charge storage layer on the lower layer dielectric film, a step of forming an upper layer dielectric film on the charge storage layer, a step of forming a memory gate electrode of a field effect transistor for memory comprising a second conductive film on the side surface of the select gate electrode, a step of removing the memory gate electrode formed on one side of the select gate electrode, and a step of removing other lower layer dielectric film, the charge storage layer and the upper layer dielectric film than the lower layer dielectric film, the charge storage layer and the upper layer dielectric film between the select gate electrode and the memory gate electrode, and between the memory gate electrode and the semiconductor substrate, the charge storage layer and the upper layer dielectric film.
The effects obtained by typical aspects of the present invention will be briefly described below.
In a split gate type MONOS memory cell, it is possible to improve the disturb tolerance at the time of program by the SSI method, without reducing a read current. Further, because the disturb tolerance of the unselected memory cell is improved, it is possible to reduce the area of the memory module.
In the embodiments described below, the invention will be described in a plurality of sections or embodiments when required as a matter of convenience. However, these sections or embodiments are not irrelevant to each other unless otherwise stated, and the one relates to the entire or a part of the other as a modification example, details, or a supplementary explanation thereof.
Also, in the embodiments described below, when referring to the number of elements (including number of pieces, values, amount, range, and the like), the number of the elements is not limited to a specific number unless otherwise stated or except the case where the number is apparently limited to a specific number in principle. The number larger or smaller than the specified number is also applicable.
Further, in the embodiments described below, it goes without saying that the components (including element steps) are not always indispensable unless otherwise stated or except the case where the components are apparently indispensable in principle.
Similarly, in the embodiments described below, when the shape of the components, positional relation thereof, and the like are mentioned, the substantially approximate and similar shapes and the like are included therein unless otherwise stated or except the case where it can be conceived that they are apparently excluded in principle. The same goes for the numerical value and the range described above.
Further, in the present embodiment, MIS•FET (Metal Insulator Semiconductor Field Effect Transistor) representing the field effect transistor is abbreviated as MIS, and an n-channel type MIS•FET is abbreviated as nMIS. In addition, an MOSFET (Metal Oxide Semiconductor FET) is a field effect transistor of a structure whose gate dielectric is made of a silicon oxide (SiO2 and the like) film, and is considered to be included in the subordinate concept of the above MIS. In addition, it is needless to mention that an MONOS type memory cell mentioned in the present embodiment is also included in the subordinate concept of the above MIS. In addition, in the present embodiment, silicon nitride includes Si3N4 of course, but also includes a dielectric film of similar composition of silicon nitride. In addition, in the present embodiment, a wafer is mainly a Si (silicon) single crystal wafer, but also it includes an SOI (Silicon On Insulator) wafer, a dielectric film substrate on which integrated circuits are formed, and the like. Further, the form thereof includes not only a circle or a rough circle, but also a square, a rectangle, and the like.
Hereinafter, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that components having the same function are denoted by the same reference symbols throughout the drawings for describing the embodiment, and the repetitive description thereof will be omitted.
First EmbodimentAn example of the structure of a split gate type MONOS memory cell according to a first embodiment of the present invention will be explained with reference to
As shown in
On the main surface of the semiconductor substrate 1 between the drain region Drm and the source region Srm, the select gate electrode CG of the above nMIS (Qnc) for selection, and the memory gate electrode MG of the above nMIS (Qnm) for memory are extended adjacently, and a plurality of the memory cells MC1 are adjacent via an element isolation region formed on the semiconductor substrate 1 in the extending direction thereof. The select gate electrode CG is arranged in the first region of the main surface of the semiconductor substrate 1, and the memory gate electrode MG is arranged in the second region that is different from the first region in the main surface of the semiconductor substrate 1. The select gate electrode CG is made of, for example, an n-type polycrystalline silicon film, and the impurities concentration thereof is, for example, around 2×1020cm−3, and the gate length thereof is, for example, around 100 to 150 nm. The memory gate electrode MG is made of, for example, an n-type polycrystalline silicon film, and the impurities concentration thereof is, for example, around 2×1020cm−3, and the gate length thereof is, for example, around 50 to 100 nm.
On the upper surface of an n+-type semiconductor region 2b comprising a part of the select gate electrode CG, the memory gate electrode MG, the source region Srm and the drain region Drm, a silicide layer 3 made of, for example, cobalt silicide, nickel silicide, titanium silicide and the like is formed. In the MONOS type memory cell, it is necessary to supply electric potential to both of the select gate electrode CG and the memory gate electrode MG, and the movement speed thereof is dependent largely on the resistance value of the select gate electrode CG and the memory gate electrode MG. Therefore, it is preferable to attain the low resistance of the select gate electrode CG and the memory gate electrode MG by forming the silicide layer 3. The thickness of the silicide layer 3 is, for example, around 20 nm.
Between the select gate electrode CG and the main surface of the semiconductor substrate, a gate dielectric 4 made of a thin silicon oxide film of thickness, for example, around 1 to 5 nm is arranged. Therefore, the select gate electrode CG is arranged on the element isolation region and the first region of the semiconductor substrate 1 via the gate dielectric 4. Furthermore, the structure of the gate dielectric 4 is a bird's beak shape, and the thickness of the gate dielectric 4 under the gate longitudinal direction end is formed thicker than that of the gate dielectric 4 under the gate longitudinal direction center.
On the main surface of the semiconductor substrate 1 under the gate dielectric 4, for example, boron is introduced and a p-type semiconductor region 5 is formed. This semiconductor region 5 is the semiconductor region for the channel formation of the nMIS (Qnc) for selection, and the threshold voltage of the nMIS (Qnc) for selection is set to a specified value by this semiconductor region 5.
The memory gate electrode MG is arranged at one side of the side surfaces of the select gate electrode CG, and the insulation between the select gate electrode CG and the memory gate electrode MG is made by a dielectric film for charge retention in which a lower layer dielectric film 6b, a charge storage layer CSL and an upper layer dielectric film 6t are laminated (hereinafter, referred to as dielectric films 6b and 6t and charge storage layer CSL). In addition, on the second region of the semiconductor substrate 1 via the dielectric films 6b and 6t and the charge storage layer CSL, the memory gate electrode MG is arranged. Meanwhile, in
The charge storage layer CSL is arranged in a state where the top and bottom thereof are pinched by the dielectric films 6b and 6t, and, for example, is made of a silicon nitride film and the thickness thereof is around 5 to 20 nm. The silicon nitride film is a dielectric film that has a discrete trap level in the film and has the function to accumulate a charge in this trap level. The dielectric films 6b and 6t are made of, for example, a silicon oxide film and the like, and the thickness of the lower layer dielectric film 6b is, for example, around 1.5 to 6 nm, and the thickness of the upper layer dielectric film 6t is, for example, around 0 to 8 nm. The dielectric films 6b and 6t may be made of a silicon oxide film including nitrogen.
On the main surface of semiconductor substrate 1, under the above lower layer dielectric film 6b, between the p-type semiconductor region 5 and the source region Srm, for example, arsenic or phosphor is introduced and an n-type semiconductor region 7 is formed. This semiconductor region 7 is a semiconductor region for the channel formation of the nMIS (Qnm) for memory, and the threshold voltage of the nMIS (Qnm) for memory is set to a specified value by this semiconductor region 7. Above the select gate electrode CG and the memory gate electrode MG, an interlayer dielectric 8 comprising a silicon nitride film 8a and a silicon oxide film 8b is formed, and a contact hole CNT reaching the drain region Drm is formed in this interlayer dielectric 8. To the drain region Drm, via a plug PLG buried in the contact hole CNT, a first metal layer M1 that extends in a second direction that is the direction intersecting to the memory gate electrode MG (or the select gate electrode CG) that extends in the first direction is connected. This wire M1 comprises a bit line of each memory cell MC1.
The characteristic of the memory cell MC1 explained in the first embodiment is that the structure of the gate dielectric 4 of the select gate electrode CG is the bird's beak shape, and in addition, the lower layer dielectric film 6b positioned between the select gate electrode CG and the charge storage layer CSL is not formed thick, but set to a specified thickness. In more concrete, (1) the thickness (toxe) of the gate dielectric 4 under the gate longitudinal direction end of the select gate electrode CG is formed thicker than that (toxc) of the gate dielectric 4 under the longitudinal direction center, and (2) the thickness of the lower layer dielectric film 6b which is positioned between the select gate electrode CG and the charge storage layer CSL and is nearest to the semiconductor substrate 1 (p well PW) (toxs) is 1.5 times or below of the thickness (toxb) of the lower layer dielectric film 6b positioned between the semiconductor substrate 1 and the charge storage layer CSL. Hereinafter, the array structure of this memory cell MC1 and the memory operations (program, program disturb, erase and read) will be explained in detail with reference to
First, an example of the array structure of the split gate type MONOS memory cell according to the first embodiment of the present invention will be explained with reference to
The select gate lines (word lines) CGL0 to CGL3 to connect the select gate electrode CG of each memory cell MC1, the memory gate lines MGL0 to MGL3 to connect the memory gate electrode MG, and the source lines SL0 and SL1 to connect the source region Srm that two adjacent memory cells share extend in the first direction respectively in parallel. Further, the bit lines BL0 and BL1 to connect the drain region Drm of the memory cell MC1 extend in the second direction, that is, in the direction intersecting perpendicularly to the select gate line CGL0 and the like. Meanwhile, these lines extend not only on the circuit diagram, but also on each memory cell MC1 or line layout in the above mentioned direction. In addition, the select gate line CGL0 and the like may comprise the select gate electrode CG, and may comprise the line to be connected to the select gate electrode CG.
To the source lines SL0 and SL1 and the memory gate lines MGL0 to MGL3, a high voltage is applied at the time of program/erase, therefore, a voltage up driver comprising a high withstand voltage MIS is connected (not shown). In addition, to the select gate lines CGL0 to CGL3, only a low voltage around 1.5V is applied, therefore, a voltage up driver with low withstand voltage and high speed is connected (not shown). 16, 32 or 64 memory cells are connected to one local bit line, and the local bit line is connected to a global bit line via the MIS to select local bit lines, and the global bit line is connected to a sense amplifier.
In the array structure shown in
Next, an example of the memory operations (program, program disturb, erase and read) of the split gate type MONOS memory cell according to the first embodiment of the present invention will be explained with reference to
The “program” and the “program disturb” will be explained.
The program is performed by so-called SSI method. The unselected cell DISTA is a memory cell connected to the memory gate line MGL, the source line SL0 and the select gate line CGL1 as with the select cell BIT1, and the unselected cells DISTB and DISTC are memory cells connected to the memory gate line MGL and the source line SL0 as with the select cell BIT1.
As shown in
In the unselected cell DISTA that receives the program disturb, the voltage Vs to be applied to the source region Srm is set 5V, the voltage Vmg to be applied to the memory gate electrode MG is set 10V, the voltage Vsg to be applied to the select gate electrode CG is set 10V, and the same voltage as that of the select cell BIT11 is applied. The voltage Vd to be applied to the drain region Drm is different from select cell BIT1, and it is set 1.5V that is larger than the voltage Vsg to be applied to the select gate electrode CG. By impressing the voltage larger than that of the select gate electrode CG to the drain region Drm, and turning off the nMIS (Qnc) for select, the program is prohibited.
In the unselected cells DISTB and DISTC that receive the program disturb, the voltage Vs to be applied to the source region Srm is set 5V, the voltage Vmg to be applied to the memory gate electrode MG is set 10V, and the same voltage as that of the select cell BIT1 is applied. The voltage Vsg to be applied to the select gate electrode CG is set unselected 0V, and the voltage Vd to be applied to the drain region Drm is set 0.4V in the case of the unselected cell connected to the bit line BL0 same as the select cell BIT1, and is set 1.5V in the case of the unselected cell connected to the bit line BL1 different from the select cell BIT1. By impressing the voltage Vd larger than the voltage Vsg to be applied to the select gate electrode CG to the drain region Drm, and turning off the nMIS (Qnc) for select, the program is prohibited.
In
As shown in
In contrast, as shown in
As shown in
Next, the “erase” will be explained.
As shown in the “erase” column of the above
When the BTBT erase is performed, the voltage Vmg to be applied to the memory gate electrode MG is set −6V, the voltage Vs to be applied to the source region Srm is set 6V, the voltage Vsg to be applied to the select gate electrode CG is set 0V, and the drain region Drm is made into a floating state. 0V is applied to the p well PW (Vwell). When the above voltage is applied, holes generated by the BTBT phenomenon at the end of the source region Srm by the voltage working between the source region Srm and the memory gate electrode MG are accelerated by the high voltage applied to the source region Srm and become hot holes, and the hot holes are pulled to the direction of the memory gate electrode MG by the high voltage applied to the memory gate electrode MG, and are injected into the charge storage layer CSL. The injected hot holes are captured by traps in the charge storage layer CSL, and the threshold voltage of the nMIS (Qnm) for memory decreases.
In the case of the FN erase where holes are injected from the memory gate electrode MG, in order for the FN tunnel injection of holes to be easily caused, the thickness of the upper layer dielectric film 6t in the memory cell MC1 of the above
In the case of the FN erase to inject holes from the semiconductor substrate 1, in order for the FN tunnel injection of holes to be easily caused, the thickness of the lower layer dielectric film 6b in the memory cell MC1 shown in the above
Next, the “read” will be explained.
As shown in the “read” column of the above
The voltage Vmg to be applied to the memory gate electrode MG at the time of the read is set between the threshold voltage of the nMIS (Qnm) for memory in the program state and the threshold voltage of the nMIS (Qmn) for memory in the erase state. When the threshold voltages in the program state and in the erase state are set 4V and −1V, respectively, the voltage Vmg at the time of the above read is the intermediate value of the both. By making it the intermediate value, even if the threshold voltage of the program state falls 2V during data retention, and even if the threshold voltage of the erase state rises 2V, it is possible to distinguish the program state and the erase state, and the margin of the data retention characteristic is made wide. If the threshold voltage of the memory cell MC1 in the erase state is lowered enough, the voltage Vmg at the time of the read can be made 0V. By making the voltage Vmg at the time of the read 0V, it is possible to avoid the read disturb, that is, the fluctuation of the threshold voltage by the voltage applied to the memory gate electrode MG.
In the memory cell MC1 according to the first embodiment, in the oxidation process to introduce the bird's beak into the gate dielectric 4 of the select gate electrode CG, a thick dielectric film is formed on the side of the select gate electrode CG, and if this thick dielectric film is left when the memory cell MC is finished, the read current decreases.
As shown in
The voltage conditions of the memory operation are shown in the above
Next, an example of the method of manufacturing the split gate type MONOS memory cell according to the first embodiment of the present invention will be explained with reference to
First, as shown in
Next, a predetermined or specified impurity is guided into the specified part of the semiconductor substrate 1 selectively with specified energy by the ion implantation method and the like, and thereby, an embedded n well NW and p well PW are formed. Then, a p-type impurity, for example, boron is ion implanted into the main surface of semiconductor substrate 1, and thereby, a p-type semiconductor region 5 for channel formation of the nMIS (Qnc) for select is formed. The ion implantation energy of this p-type impurity is, for example, around 20 keV, and the dose quantity thereof is, for example, around 1.5×1013cm−2.
Next, by performing oxidation processing to the semiconductor substrate 1, on the main surface of the semiconductor substrate 1, a gate dielectric 4 of thickness, for example 1 to 5 nm comprising a silicon oxide film is formed. Then, on the main surface of the semiconductor substrate 1, a first conductive film 9 comprising a polycrystalline silicon film having an impurity concentration of, for example, 2×1020cm−3 is accumulated. This first conductive film 9 is formed by the CVD (Chemical Vapor Deposition) method, and, the thickness thereof is, for example, around 150 to 250 nm.
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
The reason why the ISSG oxidation method is used for the film formation of the lower layer dielectric film 6b is because the single crystal silicon comprising the semiconductor substrate 1 and the polycrystalline silicon film comprising the select gate electrode CG are oxidized at about the same speed, even not at a high temperature.
Therefore, because it is possible to make the thickness (toxs) of the lower layer dielectric film 6b which is positioned at the side surface of the select gate electrode CG, and is nearest to the semiconductor substrate 1 roughly same as that (toxb) of the lower layer dielectric film 6b on semiconductor substrate 1, as explained with reference to the above
The structures of respective films comprising the dielectric films 6b and 6t and the charge storage layer CSL differ with the usage of the semiconductor device to be manufactured, therefore, only representative structures and values are described herein, but the present invention is not limited to the above structures and values.
Next, on the main surface of the semiconductor substrate 1, a second conductive film 10a comprising a polycrystalline silicon film having the impurity concentration of, for example, 2×1020cm−3 is accumulated. This second conductive film 10a is formed by the CVD method, and, the thickness thereof is, for example, around 50 to 100 nm.
Next, as shown in
Next, with a resist pattern R1 as a mask, the sidewall 10 exposing therefrom is etched, and a memory gate electrode MG comprising the sidewall 10 is formed in only the one side of the side surfaces of the select gate electrode CG. The gate length of the memory gate electrode MG is, for example, around 50 to 100 nm.
Next, as shown in
Next, after a resist pattern whose end is positioned on the top surface of the select gate electrode CG and that covers a part of the select gate electrode CG on the opposite side to the memory gate electrode MG is formed, with the select gate electrode CG, the memory gate electrode MG and the resist pattern as a mask, an n-type impurity, for example, arsenic is ion implanted to the main surface of the semiconductor substrate 1, and on the main surface of the semiconductor substrate 1, an n−-type semiconductor region 2as is formed in a self-aligning manner to the memory gate electrode MG. At this time, the ion implantation energy of this n−-type impurity is, for example, around 5 keV, and the dose quantity thereof is, for example, around 1×1015cm−2.
Next, after a resist pattern whose end is positioned in the top surface of the select gate electrode CG and that covers a part of the select gate electrode CG on the side to the memory gate electrode MG and the memory gate electrode MG is formed, with the select gate electrode CG, the memory gate electrode MG and the resist pattern as a mask, an n-type impurity, for example, arsenic is ion implanted to the main surface of the semiconductor substrate 1, and on the main surface of the semiconductor substrate 1, an n−-type semiconductor region 2ad is formed in a self-aligning manner to the select gate electrode CG. The ion implantation energy of this n-type impurity is, for example, around 7 keV, and the dose quantity thereof is, for example, around 1×1015cm−2.
Herein, the n−-type semiconductor region 2as is formed first, and then the n−-type semiconductor region 2ad is formed, but the n−-type semiconductor region 2ad may be formed first, and then the n−-type semiconductor region 2as may be formed, or the n−-type semiconductor regions 2as and 2ad may be formed at the same time. Further, after the ion implantation of the n-type impurity to form the n−-type semiconductor region 2ad, a p-type impurity, for example, boron may be ion implanted into the main surface of the semiconductor substrate 1, and a p-type semiconductor region may be formed so as to surround the lower part of the n−-type semiconductor regions 2as and 2ad. The ion implantation energy of this p-type impurity is, for example, around 20 keV, and the dose quantity thereof is, for example, around 2.5×1013cm−2.
Next, as shown in
Next, with the sidewall 11 as a mask, n-type impurities, for example, arsenic and phosphor are ion implanted into the main surface of the semiconductor substrate 1, and thereby, an n+-type semiconductor region 2b is formed on the main surface of semiconductor substrate 1 in a self-aligning manner to the select gate electrode CG and the memory gate electrode MG. The ion implantation energy of this n-type impurity is, for example, around 50 keV, and the dose quantity thereof is, for example, around 4×1015cm−2, the ion implantation energy of phosphor is, for example, around 40 keV, and the dose quantity thereof is, for example, around 5×1013cm−2. Thereby, the drain region Drm comprising the n−-type semiconductor region 2ad and the semiconductor region 2b, and the source region Srm comprising the n−-type semiconductor region 2as of the n+-type semiconductor region 2b are formed.
Next, as shown in
Next, on the main surface of the semiconductor substrate 1, an interlayer dielectric 8 comprising, for example, a silicon nitride film 8a and a silicon oxide film 8b is formed by the CVD method. Then, a contact hole CNT is formed in the interlayer dielectric 8, and a plug PLG is formed in the contact hole CNT. The plug PLG has a relatively thin barrier film comprising, for example, a laminated film of titanium and titanium nitride, and a relatively thick conductive film comprising tungsten or aluminum or the like formed so as to be covered with the barrier film. Thereafter, on the interlayer dielectric 8, a first metal layer M1 comprising, for example, tungsten, aluminum or copper or the like is formed, and the memory cell MC1 shown in the above
Thus, according to the first embodiment, the thickness (toxe) of the gate dielectric 4 under the gate longitudinal direction end of the select gate electrode CG is formed thicker than that (toxc) of the gate dielectric 4 under the gate longitudinal direction center, and the thickness of the lower layer dielectric film 6b that is positioned between the select gate electrode CG and the charge storage layer CSL and is nearest to the semiconductor substrate 1 is 1.5 times or below of the thickness of the lower layer dielectric film 6b positioned between the semiconductor substrate 1 and the charge storage layer CSL, thereby, it is possible to improve the disturb tolerance of the unselected memory cell at the time of program by the SSI method, without reducing a read current. Further, because the disturb tolerance of the unselected memory cell is improved, it is possible to reduce the area of the memory module.
Second EmbodimentIn a second embodiment, an example of the method of manufacturing a split gate type MONOS memory cell in which the formation method of the gate dielectric of nMIS for select is different from that in the first embodiment mentioned above will be explained. The method of manufacturing a split gate type MONOS memory cell by the second embodiment will be explained with reference to
As explained with the above
Next, as shown in
Next, as shown in
Thus, according to the second embodiment, because the bird's beak can be formed on the gate dielectric 4 under the gate longitudinal direction end of the select gate electrode CG, the same effect as that in the first embodiment mentioned above is provided. In addition, because the dry oxidation processing or the ISSG oxidation processing is used when the bird's beak is formed, the silicon oxide film of the bell shape is not formed like the first embodiment mentioned above at the side of the select gate electrode CG, therefore, it is possible to restrain the fluctuations of the shape and dimensions of the select gate electrode CG.
Third EmbodimentIn a third embodiment, an example of the method of manufacturing a split gate type MONOS memory cell in which the formation method of the gate dielectric of the nMIS for select is different from that in the first and second embodiments mentioned above will be explained. The method of manufacturing the split gate type MONOS memory cell according to the third embodiment will be explained with reference to
As explained with the above
Next, as shown in
Next, as shown in
Next, as shown in
Next, as shown in
Thus, according to the third embodiment, because the bird's beak can be formed onto the gate dielectric 4 under the gate longitudinal direction end of the select gate electrode CG, the same effect as the first embodiment mentioned above is provided. In addition, when the bird's beak is formed, the high temperature silicon oxide film HTO and the sidewall 13 made of a silicon nitride film are formed at the side surface of the select gate electrode CG, and the bell-shaped silicon oxide film is not formed at the side surface of the select gate electrode CG, and thereby, it is possible to restrain the fluctuations of the shape and dimensions of the select gate electrode CG.
Fourth EmbodimentIn a fourth embodiment, the bird's beak is formed only on the gate dielectric under the one end of the gate longitudinal direction of the select gate electrode CG of the nMIS for select. In the first to third embodiments mentioned above, the bird's beak is formed on the gate dielectric under both ends of the gate longitudinal direction of the select gate electrode, but even if the bird's beak is formed on only one side, it is possible to restrain the reduction of the read current, and to improve the disturb tolerance of the unselected memory cell. The method of manufacturing a split gate type MONOS memory cell according to the fourth embodiment will be explained with reference to
As explained with the above
Next, as shown in
Next, as shown in
Next, the resist pattern R2 is removed, and after the silicon nitride film 14 is removed, with the select gate electrode CG and the resist pattern as a mask, an n-type impurity, for example, arsenic or phosphor is ion implanted into the main surface of the semiconductor substrate 1, and thereby, an n-type semiconductor region 7 for the channel formation of the nMIS (Qnm) for memory is formed.
Thus, according to the fourth embodiment, because the bird's beak can be formed onto the gate dielectric 4 under the one end of the gate longitudinal direction of the select gate electrode CG, the same effect as the first embodiment mentioned above is provided. In addition, because the bell-shaped silicon oxide film is formed only at one side of the select gate electrode CG, and thereby, it is possible to restrain the fluctuations of the shape and dimensions of the select gate electrode CG more than the memory cell of the first embodiment mentioned above.
Fifth EmbodimentIn the first to fourth embodiments mentioned above, the method of manufacturing only a memory cell is described, but actually, the MIS of the peripheral circuit to be packaged together at the same time is also formed. In the MIS of the peripheral circuit, there are an MIS for core logic and a high withstand voltage MIS for high voltage control. Of these, the gate electrode of the MIS for core logic and the select gate electrode of the memory cell are not formed at the same time, and the select gate electrode of the memory cell is formed first, and then the gate electrode of the MIS for core logic is formed, and thereby it is possible to form the bird's beak on the gate dielectric of selection nMIS of the memory cell, without forming the bird's beak on the gate dielectric of the MIS for the core logic. If the bird's beak is not formed on the MIS for core logic, the ON current of the MIS for core logic does not decrease, and therefore, it is possible to secure the high speed operation of the core logic circuit. In addition, by forming the memory cell first, because heat load at the formation of the memory cell is applied before the MIS of the peripheral circuit is formed, it is possible to form the MIS of the peripheral circuit under the most suitable conditions without being influenced by the manufacturing process of the memory cell. Thereby, it is possible to form the MIS of the peripheral circuit suitable for the high speed operation.
The method of manufacturing the nMIS of peripheral circuit and the split gate type MONOS memory cell according to the fifth embodiment will be explained with reference to
First, as shown in
Next, after the gate dielectric 4 is formed on the main surface of the semiconductor substrate 1, a first conductive film 53 comprising a polycrystalline silicon film is accumulated on the main surface of the semiconductor substrate 1. Thereafter, with the resist pattern as a mask, the first conductive film 53 is processed, and thereby, a select gate electrode CG is formed in the memory cell region. Although the gate electrode of the nMIS for core logic may be formed in the peripheral circuit region at the same time, but herein, the first conductive film 53 of the peripheral circuit region is covered with the resist pattern, and the gate electrode of the nMIS for core logic is not processed. Thereafter, the exposed gate dielectric 4 is removed by, for example, a hydrofluoric acid water solution.
Next, as shown in
Next, as shown in
Next, as shown in
Thus, according to the fifth embodiment, after the memory cell is formed, the MIS of the peripheral circuit is formed, and thereby, it is possible to manufacture the semiconductor device in which the nMIS (Qnc) for select of the memory cell where the bird's beak is formed in the gate dielectric 4, and the MIS of the peripheral circuit where the bird's beak is not formed in the gate dielectric are packaged on a same substrate.
In the foregoing, the invention made by the inventors of the present invention has been concretely described based on the embodiments. However, it is needless to say that the present invention is not limited to the foregoing embodiments and various modifications and alterations can be made within the scope of the present invention.
For example, in the above embodiments, as an charge holding dielectric film of the memory cell, a charge storage layer comprising a silicon nitride film is used, but in the place of the silicon nitride film, a charge-trapping dielectric film such as an acid silicon nitride film, a tantalum oxide film, an aluminum oxide film or the like may be used. In addition, as a charge storage layer, conductive materials such as polycrystalline silicon films or the like or fine particles (dots) comprising conductive materials may be employed.
The present invention may be applied to a semiconductor memory device having a nonvolatile memory cell to store a charge into a dielectric film such as a nitride film.
Claims
1. A semiconductor memory device comprising nonvolatile memory cells including a first field effect transistor in a first region of the main surface of a semiconductor substrate, and a second field effect transistor which is adjacent to the first field effect transistor in a second region, wherein
- a first gate electrode of the first field effect transistor formed in the first region, a second gate electrode of the second field effect transistor formed in the second region, a first gate dielectric formed between the semiconductor substrate and the first gate electrode, a charge storage layer formed between the semiconductor substrate and the second gate electrode and between the first gate electrode and the second gate electrode, and a first dielectric film formed between the semiconductor substrate and the charge storage layer and between the first gate electrode and the charge storage layer are arranged,
- the thickness of the first gate dielectric under the gate longitudinal direction end of the first gate electrode is thicker than that of the first gate dielectric under the gate longitudinal direction center of the first gate electrode, and the thickness of the first dielectric film that is positioned between the first gate electrode and the charge storage layer and is nearest to the semiconductor substrate, is 1.5 times or below of the thickness of the first dielectric film between the semiconductor substrate and the charge storage layer.
2. The semiconductor memory device according to claim 1, wherein the thickness of the first gate dielectric under the gate longitudinal direction end of the first gate electrode is thicker by 0.5 nm or more than that of the first gate dielectric under the gate longitudinal direction center of the first gate electrode.
3. The semiconductor memory device according to claim 1, further comprising
- a third field effect transistor formed in a third region of the main surface of the semiconductor substrate for performing a logic operation,
- a third gate electrode of the third field effect transistor formed in the third region, and
- a second gate dielectric formed between the semiconductor substrate and the third gate electrode are arranged, and wherein
- the difference between the thickness of the second gate dielectric under the gate longitudinal direction end of the third gate electrode and the thickness of the second gate dielectric under the gate longitudinal direction center of the third above gate electrode is 0.5 nm or below.
4. The semiconductor memory device according to claim 1, wherein the thickness of the first gate dielectric under one gate longitudinal direction end of the first gate electrode is thicker than that of the first gate dielectric under the gate longitudinal direction center of the first gate electrode.
5. The semiconductor memory device according to claim 1, wherein the charge storage layer is a silicon nitride film, an silicon oxynitride film, a tantalum oxide film or an aluminum oxide film.
6. The semiconductor memory device according to claim 1, wherein the first dielectric film is a silicon oxide film.
7. The semiconductor memory device according to claim 1, wherein a second dielectric film is arranged between the second gate electrode and the charge storage layer.
8. The semiconductor memory device according to claim 7, wherein the second dielectric film is a silicon oxide film, a dielectric film in which a silicon nitride film is inserted in between silicon oxide films, or a dielectric film in which an amorphous silicon film is inserted in between silicon oxide films.
9. The semiconductor memory device according to claim 1, wherein information is written by injecting hot electrons into the charge storage layer by an SSI method.
10. The semiconductor memory device according to claim 1, wherein information is erased by injecting hot holes into the charge storage layer by a BTBT phenomenon.
11. A method of manufacturing a semiconductor memory device for forming nonvolatile memory cells including a first field effect transistor in a first region of the main surface of a semiconductor substrate, and a second field effect transistor which is adjacent to the first field effect transistor in a second region, the method comprising the steps of:
- (a) forming a first gate dielectric in the main surface of the semiconductor substrate in the first region;
- (b) forming the first gate electrode of the first field effect transistor comprising the first conductive film via the first gate dielectric in the first region, after forming the first conductive film on the main surface of the semiconductor substrate;
- (c) removing the first gate dielectric of other regions than the first gate dielectric under the first gate electrode;
- (d) performing a first oxidation processing to the semiconductor substrate, and making the thickness of the first gate dielectric under the gate longitudinal direction end of the first gate electrode thicker than that of the first gate dielectric under the gate longitudinal direction center of the first gate electrode;
- (e) performing a second oxidation processing to the semiconductor substrate by removing the whole or part of an oxide film formed by the first oxidation processing, after the step (d), and thereby forming a first dielectric film;
- (f) forming a charge storage layer on the first dielectric film, after the step (e);
- (g) forming the second conductive film on the main surface of the semiconductor substrate after the step (f), processing the second conductive film by anisotropic etching, and thereby forming sidewalls comprising the second conductive films on both of the sides of the first gate electrode;
- (h) removing the sidewall formed on one side of the first gate electrode, and making the sidewall remaining on the other side of the first gate electrode a second gate electrode; and
- (i) removing the first dielectric film and the charge storage layer of other regions than the first dielectric film and the charge storage layer formed between the first gate electrode and the second gate electrode, and in a second region.
12. The method of manufacturing a semiconductor memory device according to claim 11, wherein, in the step (e), the first dielectric film is formed so that the thickness of the first dielectric film that is positioned between the first gate electrode and the charge storage layer and is nearest to the semiconductor substrate, is 1.5 times or below of that of the first dielectric film between the semiconductor substrate and the charge storage layer.
13. The method of manufacturing a semiconductor memory device according to claim 11, wherein the thickness of the first gate dielectric under the gate longitudinal direction end of the first gate electrode is formed thicker by 0.5 nm or more than that of the first gate dielectric under the gate longitudinal direction center of the first gate electrode.
14. The method of manufacturing a semiconductor memory device according to claim 11, further comprising the following step between the step (f) and the step (g):
- (j) forming a second dielectric film on the charge storage layer.
15. The method of manufacturing a semiconductor memory device according to claim 11, wherein the second oxidation processing is performed to the semiconductor substrate by performing ISSG oxidation processing.
16. The method of manufacturing a semiconductor memory device according to claim 11, wherein the first oxidation processing is wet oxidation processing.
17. The method of manufacturing a semiconductor memory device according to claim 11, wherein the first oxidation processing is dry oxidation processing.
18. The method of manufacturing a semiconductor memory device according to claim 17, wherein, in the step (c), the first gate dielectric under the gate longitudinal direction end of the first gate electrode is further etched by 3 to 20 nm from the end of the first gate electrode.
19. The method of manufacturing a semiconductor memory device according to claim 11, wherein the step (d) further including the steps of:
- (d1) forming a third dielectric film on the main surface of the semiconductor substrate;
- (d2) forming sidewalls comprising a fourth dielectric film via the third dielectric film on the sides of the first gate electrode;
- (d3) removing the third dielectric film, until the first gate dielectric under the first gate electrode is exposed; and
- (d4) performing dry oxidation processing to the semiconductor substrate, and forming the thickness of the first gate dielectric under the gate longitudinal direction end of the first gate electrode thicker than that of the first gate dielectric under the gate longitudinal direction center of the first gate electrode, and further,
- the step (e) including a step of
- (e1) removing the third dielectric film of other regions than the first gate dielectric under the first gate electrode, the sidewalls, and the oxide film formed by the dry oxidation processing.
Type: Application
Filed: Aug 14, 2008
Publication Date: Feb 26, 2009
Applicant:
Inventors: TETSUYA ISHIMARU (Tokyo), YOSHIYUKI KAWASHIMA (Hitachinaka), YASUHIRO SHIMAMOTO (Tokorozawa), KAN YASUI (Kodaira), TSUYOSHI ARIGANE (Akishima), TOSHIYUKI MINE (Fussa)
Application Number: 12/191,958
International Classification: H01L 29/792 (20060101); H01L 21/336 (20060101);